Motor vehicles having a belt-driven drive are conventional. For example, German Patent Application No. DE 101 53 329 A1 describes a belt transmission device which has a pulley of a rotating electric machine for transmitting a starter force to an engine, a motor pulley for transmitting the starter force to the engine and also for transmitting a rotational force of the engine to a component part and an auxiliary pulley which is driven to rotate by the force of the motor pulley in order to drive the component part in the process. Furthermore, the conventional device has a belt, which is wound around the pulley of the rotating electric machine, the motor pulley and the auxiliary pulley, and a belt tension setting element for tensioning the belt in order to set the tension of the belt for a plurality of operating states. This tension setting element functions in such a way that the belt tension is set to a high belt tension value, when the engine is started by the rotating electric machine, and is set to a low belt tension value, when the engine is in a subsequent normal operation. This setting of the belt tension is controlled by a control unit which is supplied with sensor signals.